The Islands Provincial Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Islands Provincial Park clear sky chart from 2005-11-06 to 2025-07-06.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	22% 12% 3 8% 5% 4 4 3 4 6% 29%	120798
	Night	22% 12% 4 9% 5% 4 4 3 5% 6% 28%	118078
Transparency	Day	56% 3 10% 19% 11% 1	124417
	Night	56% 3 10% 20% 10% 1	122608
Seeing	Day	28% 16% 32% 17% 6% 1	18049
	Night	27% 14% 29% 22% 7% 1	25584

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 18% 6% 17% 7% 4 4 3 4 5% 15%	3636
	11th to 20th	Day	16% 17% 7% 19% 7% 6% 4 3 4 4 13%	4027
	21st to end	Day	17% 15% 5% 14% 8% 5% 4 3 4 5% 19%	4466
February	1st to 10th	Day	20% 18% 5% 10% 7% 6% 5% 3 4 5% 18%	1800
	11th to 20th	Day	18% 11% 4 13% 8% 6% 4 3 4 6% 21%	1753
	21st to end	Day	15% 15% 5% 9% 6% 4 4 3 6% 7% 27%	1575
March	1st to 10th	Day	25% 16% 4 11% 6% 4 4 3 4 4 20%	4882
	11th to 20th	Day	18% 19% 4 7% 4 4 4 3 4 5% 28%	4980
	21st to end	Day	29% 12% 5% 10% 5% 4 4 3 3 4 21%	5466
April	1st to 10th	Day	25% 16% 2 7% 4 4 3 2 4 5% 27%	2321
	11th to 20th	Day	21% 10% 3 6% 4 4 4 3 4 6% 35%	2507
	21st to end	Day	24% 9% 2 6% 4 3 3 3 5% 6% 36%	2600
May	1st to 10th	Day	28% 14% 4 9% 4 4 4 3 4 4 23%	5886
	11th to 20th	Day	25% 12% 3 7% 4 4 4 3 5% 6% 28%	6133
	21st to end	Day	21% 10% 3 8% 4 4 4 3 5% 7% 31%	6948
June	1st to 10th	Day	26% 9% 2 6% 4 4 4 3 5% 6% 31%	2800
	11th to 20th	Day	21% 9% 3 5% 4 3 3 2 5% 6% 38%	2960
	21st to end	Day	27% 8% 2 5% 5% 4 4 4 4 8% 29%	3000
July	1st to 10th	Day	25% 9% 3 6% 4 3 4 4 6% 6% 31%	4813
	11th to 20th	Day	31% 9% 2 5% 3 3 4 3 4 7% 28%	4358
	21st to end	Day	21% 9% 3 6% 4 4 4 3 5% 7% 33%	4467
August	1st to 10th	Day	31% 10% 3 6% 3 3 3 3 4 6% 28%	4105
	11th to 20th	Day	18% 7% 3 7% 4 4 4 3 5% 7% 36%	4045
	21st to end	Day	13% 6% 2 5% 3 3 4 3 5% 8% 48%	4418
September	1st to 10th	Day	16% 7% 2 5% 4 4 3 3 5% 7% 44%	2280
	11th to 20th	Day	19% 6% 3 5% 3 4 3 3 4 5% 45%	2109
	21st to end	Day	20% 8% 2 5% 4 4 3 3 4 6% 41%	2088
October	1st to 10th	Day	20% 7% 2 5% 4 4 4 3 4 7% 38%	1900
	11th to 20th	Day	20% 7% 2 6% 4 5% 4 4 5% 7% 36%	1900
	21st to end	Day	21% 9% 3 7% 6% 4 5% 3 5% 6% 32%	2086
November	1st to 10th	Day	21% 10% 3 6% 5% 3 4 4 5% 6% 34%	1701
	11th to 20th	Day	21% 13% 3 8% 6% 4 4 3 5% 7% 26%	1600
	21st to end	Day	21% 14% 3 9% 7% 5% 5% 4 4 5% 23%	1600
December	1st to 10th	Day	24% 12% 4 12% 4 4 4 3 5% 6% 20%	2610
	11th to 20th	Day	30% 11% 3 7% 5% 5% 5% 3 4 6% 22%	2996
	21st to end	Day	21% 15% 6% 8% 4 4 4 3 4 5% 27%	3982
January	1st to 10th	Night	15% 18% 7% 19% 6% 5% 4 3 4 4 16%	6326
	11th to 20th	Night	16% 14% 6% 16% 6% 5% 5% 4 5% 5% 16%	5858
	21st to end	Night	15% 14% 5% 14% 6% 5% 5% 4 5% 6% 21%	6490
February	1st to 10th	Night	19% 14% 5% 11% 7% 5% 4 4 5% 5% 21%	2600
	11th to 20th	Night	18% 12% 4 11% 8% 6% 5% 5% 6% 7% 21%	2533
	21st to end	Night	14% 12% 4 8% 6% 5% 5% 4 5% 8% 30%	2050
March	1st to 10th	Night	24% 14% 5% 9% 7% 5% 4 3 3 4 22%	4957
	11th to 20th	Night	19% 16% 5% 8% 5% 3 4 4 5% 6% 26%	4979
	21st to end	Night	31% 11% 4 7% 3 2 2 2 4 5% 28%	5466
April	1st to 10th	Night	24% 13% 3 7% 4 4 3 2 5% 5% 30%	2077
	11th to 20th	Night	24% 10% 2 5% 3 4 3 3 4 7% 34%	1838
	21st to end	Night	24% 9% 3 6% 4 3 4 3 4 7% 33%	1800
May	1st to 10th	Night	30% 14% 3 7% 4 3 4 3 5% 5% 24%	4054
	11th to 20th	Night	25% 13% 3 7% 3 3 3 2 4 5% 32%	3772
	21st to end	Night	21% 14% 3 7% 4 4 3 3 4 5% 32%	3948
June	1st to 10th	Night	25% 9% 3 7% 3 3 4 3 5% 8% 30%	1600
	11th to 20th	Night	20% 10% 3 6% 4 4 4 3 4 6% 35%	1453
	21st to end	Night	28% 9% 3 6% 4 4 4 3 5% 6% 27%	1400
July	1st to 10th	Night	30% 12% 4 7% 4 3 3 3 5% 6% 23%	2245
	11th to 20th	Night	34% 11% 3 5% 4 3 3 3 5% 7% 23%	2591
	21st to end	Night	22% 10% 2 6% 4 4 4 3 5% 7% 32%	3087
August	1st to 10th	Night	30% 11% 3 7% 4 3 3 2 3 7% 29%	2825
	11th to 20th	Night	21% 10% 2 7% 5% 3 4 3 5% 7% 33%	2782
	21st to end	Night	13% 9% 2 5% 3 3 4 3 5% 8% 46%	3238
September	1st to 10th	Night	17% 8% 2 5% 4 4 3 3 5% 7% 42%	1900
	11th to 20th	Night	20% 7% 2 4 3 3 3 4 5% 6% 44%	2066
	21st to end	Night	21% 8% 3 6% 3 3 3 3 5% 6% 39%	2091
October	1st to 10th	Night	21% 7% 3 6% 4 4 4 3 4 7% 38%	2280
	11th to 20th	Night	19% 7% 2 5% 3 4 3 3 5% 6% 43%	2280
	21st to end	Night	23% 8% 2 6% 3 4 4 3 4 7% 35%	2508
November	1st to 10th	Night	18% 7% 3 6% 4 4 4 3 5% 7% 38%	2595
	11th to 20th	Night	20% 11% 3 7% 5% 5% 5% 4 5% 7% 28%	2800
	21st to end	Night	20% 13% 3 8% 4 4 5% 4 6% 6% 27%	2800
December	1st to 10th	Night	16% 12% 4 12% 6% 5% 5% 4 5% 7% 22%	4580
	11th to 20th	Night	24% 12% 3 7% 4 4 4 4 5% 6% 27%	5213
	21st to end	Night	24% 12% 4 9% 6% 4 3 3 3 4 28%	6996

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	68% 3 10% 15% 4	3637
	11th to 20th	Day	72% 3 9% 12% 4	4060
	21st to end	Day	63% 2 8% 15% 11% 1	4466
February	1st to 10th	Day	66% 3 10% 13% 8% 1	1800
	11th to 20th	Day	61% 3 11% 16% 7% 1	1761
	21st to end	Day	54% 3 11% 20% 9% 3	1575
March	1st to 10th	Day	67% 2 8% 13% 9% 2	4886
	11th to 20th	Day	57% 2 14% 17% 9% 1	4980
	21st to end	Day	66% 2 6% 15% 10% 1	5466
April	1st to 10th	Day	59% 2 9% 15% 14% 1	2321
	11th to 20th	Day	51% 4 9% 21% 14% 1	2507
	21st to end	Day	49% 3 11% 21% 15% 2	2600
May	1st to 10th	Day	66% 2 8% 17% 6%	5897
	11th to 20th	Day	59% 3 9% 19% 8% 2	6137
	21st to end	Day	54% 2 13% 17% 11% 2	6948
June	1st to 10th	Day	54% 3 9% 22% 11% 1	2800
	11th to 20th	Day	49% 2 11% 22% 14% 2	2960
	21st to end	Day	55% 3 12% 18% 10% 1	3000
July	1st to 10th	Day	54% 4 11% 18% 12% 2	4738
	11th to 20th	Day	57% 3 9% 22% 8% 1	4282
	21st to end	Day	50% 4 12% 22% 11% 1	4325
August	1st to 10th	Day	59% 3 9% 19% 9% 1	4092
	11th to 20th	Day	46% 4 13% 28% 8%	4084
	21st to end	Day	34% 4 12% 29% 20% 1	4418
September	1st to 10th	Day	41% 3 11% 25% 18% 2	2280
	11th to 20th	Day	42% 3 10% 25% 17% 3	2109
	21st to end	Day	45% 3 7% 24% 18% 2	2088
October	1st to 10th	Day	44% 6% 11% 26% 13% 1	3160
	11th to 20th	Day	40% 3 9% 25% 22% 1	3140
	21st to end	Day	44% 4 12% 25% 12% 4	3412
November	1st to 10th	Day	51% 3 13% 22% 10% 1	1701
	11th to 20th	Day	56% 4 11% 19% 10% 1	1600
	21st to end	Day	60% 4 12% 19% 5% 1	1600
December	1st to 10th	Day	62% 3 12% 18% 4	2610
	11th to 20th	Day	62% 3 11% 14% 10% 1	2995
	21st to end	Day	58% 2 12% 18% 9% 1	3982
January	1st to 10th	Night	70% 2 8% 16% 4 1	6326
	11th to 20th	Night	65% 4 10% 16% 5%	5900
	21st to end	Night	60% 3 11% 15% 10%	6490
February	1st to 10th	Night	63% 3 11% 15% 8% 1	2600
	11th to 20th	Night	60% 3 10% 19% 8% 1	2536
	21st to end	Night	52% 3 11% 22% 11% 1	2050
March	1st to 10th	Night	65% 3 6% 12% 12% 2	4966
	11th to 20th	Night	60% 2 13% 17% 7% 1	4980
	21st to end	Night	60% 2 7% 19% 11% 1	5466
April	1st to 10th	Night	57% 2 8% 16% 13% 3	2077
	11th to 20th	Night	50% 3 8% 25% 12% 1	1838
	21st to end	Night	52% 3 10% 20% 12% 3	1800
May	1st to 10th	Night	65% 1 9% 16% 8% 1	4060
	11th to 20th	Night	57% 2 8% 22% 9% 2	3773
	21st to end	Night	56% 3 10% 22% 9% 1	3949
June	1st to 10th	Night	54% 2 7% 26% 10% 1	1600
	11th to 20th	Night	51% 3 11% 21% 13% 1	1453
	21st to end	Night	60% 4 8% 15% 11% 1	1400
July	1st to 10th	Night	64% 3 8% 16% 9%	2210
	11th to 20th	Night	64% 3 7% 15% 9% 1	2544
	21st to end	Night	54% 5% 10% 20% 10% 1	2989
August	1st to 10th	Night	60% 2 9% 20% 9%	2813
	11th to 20th	Night	51% 5% 13% 24% 6%	2809
	21st to end	Night	38% 3 11% 29% 18% 1	3237
September	1st to 10th	Night	43% 3 8% 27% 17% 3	1900
	11th to 20th	Night	42% 3 8% 27% 19% 2	2066
	21st to end	Night	48% 2 6% 26% 17% 1	2091
October	1st to 10th	Night	46% 5% 11% 23% 13% 1	3800
	11th to 20th	Night	34% 2 11% 27% 25% 1	3779
	21st to end	Night	41% 2 11% 28% 17% 1	4120
November	1st to 10th	Night	46% 3 14% 25% 11% 1	2595
	11th to 20th	Night	54% 3 12% 20% 10%	2800
	21st to end	Night	54% 5% 15% 19% 7%	2800
December	1st to 10th	Night	56% 3 12% 24% 5%	4580
	11th to 20th	Night	55% 3 12% 16% 12%	5215
	21st to end	Night	60% 2 10% 17% 10% 2	6996

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	31% 25% 28% 13% 3	400
	11th to 20th	Day	31% 21% 30% 15% 3	400
	21st to end	Day	22% 28% 31% 15% 3	440
February	1st to 10th	Day	32% 24% 29% 14% 3	400
	11th to 20th	Day	32% 25% 28% 12% 3	396
	21st to end	Day	28% 21% 33% 15% 2	377
March	1st to 10th	Day	33% 20% 33% 11% 2	500
	11th to 20th	Day	31% 22% 32% 11% 4 1	500
	21st to end	Day	30% 23% 32% 10% 5% 1	550
April	1st to 10th	Day	35% 25% 29% 10% 1	500
	11th to 20th	Day	30% 20% 37% 11% 2	492
	21st to end	Day	29% 20% 33% 12% 5% 1	500
May	1st to 10th	Day	31% 21% 32% 13% 2 1	503
	11th to 20th	Day	28% 18% 30% 19% 4 1	643
	21st to end	Day	30% 12% 33% 18% 6% 1	790
June	1st to 10th	Day	32% 11% 33% 19% 5% 1	730
	11th to 20th	Day	24% 12% 34% 22% 8% 1	730
	21st to end	Day	33% 9% 31% 21% 5% 1	730
July	1st to 10th	Day	28% 8% 29% 25% 9% 1	695
	11th to 20th	Day	30% 5% 32% 23% 10% 1	625
	21st to end	Day	24% 7% 35% 25% 8% 1	532
August	1st to 10th	Day	20% 8% 37% 24% 9% 2	486
	11th to 20th	Day	25% 8% 33% 20% 11% 2	479
	21st to end	Day	22% 8% 33% 21% 12% 3	539
September	1st to 10th	Day	20% 11% 33% 27% 8% 2	490
	11th to 20th	Day	25% 10% 31% 21% 9% 3	490
	21st to end	Day	22% 12% 36% 21% 7% 3	488
October	1st to 10th	Day	22% 11% 34% 21% 10% 2	390
	11th to 20th	Day	21% 18% 31% 21% 7% 2	390
	21st to end	Day	25% 17% 34% 17% 6%	429
November	1st to 10th	Day	24% 20% 32% 17% 7% 1	395
	11th to 20th	Day	30% 25% 27% 12% 5%	400
	21st to end	Day	31% 22% 28% 17% 3 1	400
December	1st to 10th	Day	37% 17% 29% 15% 3	400
	11th to 20th	Day	39% 23% 23% 12% 4	400
	21st to end	Day	30% 23% 28% 14% 3 1	440
January	1st to 10th	Night	29% 22% 29% 16% 4	895
	11th to 20th	Night	29% 17% 29% 22% 4	800
	21st to end	Night	24% 24% 31% 18% 4	880
February	1st to 10th	Night	29% 22% 28% 19% 2	800
	11th to 20th	Night	27% 24% 32% 15% 2	783
	21st to end	Night	23% 17% 35% 18% 6%	660
March	1st to 10th	Night	28% 19% 33% 17% 3	800
	11th to 20th	Night	24% 18% 33% 19% 6%	800
	21st to end	Night	26% 19% 32% 17% 5%	880
April	1st to 10th	Night	31% 14% 34% 18% 3	677
	11th to 20th	Night	29% 14% 37% 16% 3 1	594
	21st to end	Night	30% 10% 30% 22% 7% 1	600
May	1st to 10th	Night	32% 11% 33% 19% 5% 1	600
	11th to 20th	Night	29% 10% 31% 24% 5% 1	592
	21st to end	Night	30% 7% 31% 24% 7% 1	649
June	1st to 10th	Night	29% 8% 33% 26% 5%	600
	11th to 20th	Night	24% 6% 31% 31% 7%	453
	21st to end	Night	34% 3 28% 28% 7% 1	400
July	1st to 10th	Night	31% 2 26% 31% 9% 1	380
	11th to 20th	Night	28% 3 29% 30% 10%	539
	21st to end	Night	29% 4 28% 33% 7%	623
August	1st to 10th	Night	22% 4 29% 35% 9% 1	568
	11th to 20th	Night	23% 6% 23% 34% 13% 1	562
	21st to end	Night	23% 4 25% 29% 17% 2	627
September	1st to 10th	Night	20% 6% 29% 32% 11% 2	570
	11th to 20th	Night	23% 6% 25% 27% 15% 3	736
	21st to end	Night	26% 8% 26% 26% 13% 2	760
October	1st to 10th	Night	26% 7% 29% 28% 11% 1	760
	11th to 20th	Night	23% 16% 26% 24% 9% 2	760
	21st to end	Night	28% 16% 27% 24% 6%	836
November	1st to 10th	Night	25% 14% 28% 24% 8% 1	810
	11th to 20th	Night	26% 20% 28% 20% 6%	900
	21st to end	Night	28% 21% 27% 18% 6%	900
December	1st to 10th	Night	31% 17% 29% 18% 5%	900
	11th to 20th	Night	31% 24% 28% 14% 3	900
	21st to end	Night	30% 21% 26% 18% 4	990

Page generated at 2025-07-03 02:30:18. Version ac07

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